Adc manual

Experiment no. 1Title: To Study the Operation of a DSB Amplitude Modulator

Objectives:

To generate amplitude modulated wave.

To determine the percentage modulation.

Aim:

A1. At the end of the session the student will be able to plan for conducting a lab experiment before doing the experiment.

A2. At the end of the session the student will be able to select suitable equipment, instruments and components/materials.

A3. At the end of the session the student will be able to set and handle machines/equipment / instruments with care & safety.

A4. At the end of the session the student will be able to demonstrate a newly acquired skill in making a useful engineering using PDCA [Plan, Do, Check & Act] cycle.

A5. At the end of the session the student will be able to Plan & execute the problem solving and other activities as a leader or a member of the team.

Inputs:

Equipment and components required: ACL01 trainer Kit, 20MHz CRO, power supply,

connecting wires and frequency counter.

General Instructions: You will plan for Experiment after self study of Theory given below,

before entering in the Lab.

Theory: Amplitude Modulation is defined as a process in which the amplitude of the carrier

wave c(t) is varied linearly with the instantaneous amplitude of the message signal m(t).The

standard form of an amplitude modulated (AM) wave is defined by

s(t) =Ac [1+K am(t)cos2 π f c t]

Where

K a is a constant called the amplitude sensitivity of the modulator.

The demodulation circuit is used to recover the message signal from the incoming AM wave at

the receiver. An envelope detector is a simple and yet highly effective device that is well suited

for the demodulation of AM wave, for which the percentage modulation is less than

100%.Ideally, an envelope detector produces an output signal that follows the envelop of the

input signal wave form exactly; hence, the name. Some version of this circuit is used in almost

all commercial AM radio receivers.

The Modulation Index is defined as,

M = Emax−Emin

Emax+ Emin

Where Emax∧Emin are the maximum and minimum amplitudes of the modulated wave.

Block Diagram:

Fig.1. Block Diagram for AM Technique

Procedure:

1. The circuit is connected as per the circuit diagram shown in Fig.1 .

2. Switch on the power supply.

3. Apply sinusoidal signal of 1 KHz frequency and amplitude 0.5 Vp-p as modulating

signal.

4. VCO: LEVEL about 1 Vp-p; frequency about 450 KHz, switchon 500 KHz.

5. Now change the amplitude of the modulating signal and note downvalues ofEmax∧Emin.

5. Calculate modulation index using equation.

6. Repeat step 5 by varying frequency of the modulating signal.

7. Plot the graphs: Modulation index vs. Amplitude & Frequency

8. Vary the amplitude of the modulating signal and check the following three conditions:

modulation percentage lower then 100%, equal to 100% and less then 100%.

Waveforms and graphs:

Observation

Table1

f m=1 KHz , f c=450 KHz , Ac=1V(p-p)

Sr. no V M Emax Emin M %MX100

Table2

f m=1 KHz , f c=500 KHz , A c=1V(p-p)

Sr. no V M Emax Emin M %MX100

Do and Don’ts to be strictly observed during experiment:

Do’s :

1. Before making the connection, identify the components leads, terminal or pins before

making the connections.

2. Before connecting the power supply to the circuit, measure voltage by

voltmeter/multimeter.

3. Use sufficiently long connecting wires, rather than joining two or three small ones.

4. The circuit should be switched off before changing any connection.

Don’ts:

1. Avoid loose connections and short circuits on the bread board.

2. Do not exceed the voltage while taking the readings.

3. Any live terminal shouldn't be touched while supply is on.

Experiment no. 2Title: To Study the Operation of a SSB modulation

Objectives:

To study Single Side Band generation.

Aim:

A1. At the end of the session the student will be able to plan for conducting a lab experiment

before doing the experiment.





Inputs:

Equipment and components required: ACL01 trainer Kit, 20MHz CRO, power supply,

connecting wires and frequency counter.

General Instructions: You will plan for Experiment after self study of Theory given below,

before entering in the Lab.

Theory: SSB is a much more efficient mode than AM since all of the transmitter's power goes

into transmitting useful intelligence. A SSB signal also occupies only about half the frequency

space of a comparable AM signal. However, SSB transmitters and receivers are far more

complicated than those for AM.

Consider the baseband message signal m(t) with the frequency spectrum M() shown in part (A)

of the fig.1. in the next page. Assuming that the signal m(t) is a real signal, the magnitude of its

spectrum is an even function and the phase of its spectrum is an odd function (so, the information

contained in the part of the spectrum with positive frequency is exactly the same as the

information contained in the part with negative frequency). The spectrum M() can be split into

two parts called M+() and M–() as shown in parts (B) and (C). and SSB signal is shown in

(E) and (F)

The equation for the USB and LSB is given in the following equations:

gUSB( t )=12

m( t )e jωC t+1

2jmh( t )e jωC t

+12

m( t )e− jωC t−1

2jmh( t )e− jωC t

=m( t )cos (ωC t )−mh( t )sin( ωC t )

gLSB( t )=12

m( t )e jωCt−1

2jmh( t )e jωC t

+12

m( t )e− jωCt+1

2jmh( t )e− jωC t

=m( t )cos (ωC t )+mh( t )sin (ωC t )

The most common envelope detector consists of a diode followed by a RC filter fig. 1 its

operation is analogous to one of the half wave rectifier, as the output voltage follows the

maximum values of the carrier. As the amplitude of the carrier is variable, by properly choosing

R and C, the output of the detector can be faithfully reproduce these variation.

Circuit Diagram:

Fig.1. Block Diagram for SSB AM Generation Technique

Procedure:

1. The circuit is connected as per the circuit diagram shown in Fig.3 .

2. Switch on the power supply.

3. Connect o/p of the function generator section ACL01 OUT post to the i/p of

balance modulator1 SIGNAL IN post.

4. Connect o/p of VCO (ACL01) OUT post to the i/p of balance modulator1 CARRIER

IN post.

5. Switch on the power supply and carry out the following presetting:

FUNCTION GENERATOR: sin level about 0.5 Vp-p; frequency 1 KHz. and VCO:

level about 2 Vp-p; frequency 850 KHz, switch on 1500KHz.

BALANCE MODULATOR1: CARRIER NULL completely rotates clockwise or

anticlockwise, so that the modulator is “unbalanced” and an AM signal with not

suppressed carrier is obtained across the output: adjust OUTLEVEL to obtain an AM

signal across the output whose amplitude is about 100m Vp-p.

6. Connect local oscillator OUT post to LO IN of the mixer section.

7. Connect balance modulator1 out to RF IN of the mixer section in ALC-02.

8. Connect mixer out to IF IN of first IF AMPLIFIER in ALC-02.

9. Connect IF OUT1 of 1st IF to IF IN 1 and IF OUT2 of 1st IF to IF N 2 of 2nd IF

AMPLIFIER.

10. Connect OUT post of 2nd IF amplifier to IN post of envelope detector.

11. Connect post AGC1 to post AGC2 and jumper as per diagram.

12. Observe the output as per given diagram.

Waveforms and graphs:

Fig.2. AM signal


Do’s:

1. Before making the connection, identify the components leads, terminal or pins

before making the connections.



3. Use sufficiently long connecting wires, rather than joining two or three small

ones.


Don’ts:




Experiment 3Objective: Study of Frequency Modulation using Varactor modulator

Aim:

A1. At the end of the session the student will be able to plan for conducting a lab experiment

before doing the experiment.





Equipments Required:

1. ST2203 tech book with power supply cord

2. Oscilloscope with connecting probe

3. Patch Cords

Connection Diagram:

Procedure :

This experiment investigates how ST2203’s character modulator circuit performs frequency

modulation. This circuit modulates the frequency of a carrier sine wave, according to the audio

signal applied to its modulating input.

1. Ensure that the following initial conditions exist on the ST2202 board.

a. All Switched Faults in ‘Off’ condition.

b. Amplitude potentiometer (in mixer amplifier block) in fully clockwise position.

c. VCO switch (in phase locked loop detector block) in ‘Off’ position.

2. Make the connections as shown in figure

3. Switch On the power.

4. Turn the audio oscillator block’s amplitude potentiometer to its fully clockwise position, and

examine the block’s output TP1 on an Oscilloscope. This is the audio frequency sine wave,

which will be used as our modulating signal. Note that the sine wave’s frequency can be adjusted

from about 300Hz to approximately 3.4 KHz, by adjusting the audio oscillator’s frequency

potentiometer. Note also that the amplitude of this modulating signal is adjusted by audio

oscillator amplitude potentiometer Leave the amplitude potentiometer in minimum position.

5. Connect the output socket of the audio oscillator block to the audio input socket of the

modulator circuit’s block.

6. Set the reactance / varactor switch to the varactor position. This switch selects the varactor

modulator and also disables the reactance modulator to prevent any interference between the two

circuits.

7. The output signal from the varactor modulator block appears at TP24 before being buffered

and amplified by the mixer/amplifier block, any capacitive loading (e.g. due to Oscilloscope

probe) may slightly affect the modulators output frequency. In order to avoid this problem we

monitor the buffered FM output signal the mixer / amplifier block at TP34.

8. Put the varactor modulator’s carrier frequency potentiometer in its midway position, and then

examine TP34. Note that it is a sine wave of approximately

1.2 Vpp, centered on 0V. This is our FM carrier, and it is un-modulated since the varactor

modulators audio input signal has zero amplitude

9. The amplitude of the FM carrier (at TP34) is adjustable by means of the mixer/amplifier

block’s amplitude potentiometer, from zero to its potentiometer level. Try turning this

potentiometer slowly anticlockwise, and note that the amplitude of the FM signal can be reduced

to zero. Return the amplitude potentiometer to its fully clockwise position.

10. Try varying the carrier frequency potentiometer and observe the effects.

11. Also, see the effects of varying the amplitude and frequency potentiometer in the audio

oscillator block.

12. Turn the carrier frequency potentiometer in the charactor modulator block slowly clockwise

and note that in addition to the carrier frequency increasing there is a decrease in the amount of

frequency deviation that is present.

13. Return the carrier frequency potentiometer to its midway position, and monitor the audio

input (at TP6) and the FM output (at TP34) triggering the Oscilloscope on the audio input signal.

Turn the audio oscillator’s amplitude potentiometer throughout its range of adjustment, and note

that the amplitude of the FM output signal does not change. This is because the audio

information is contained entirely in the signals frequency and not in its amplitude.

14. By using the optional audio input module ST2108 the human voice can be used as the audio

modulating signal, instead of using ST2203’s audio oscillator block. If you have an audio input

module, connect the module’s output to the audio input socket in the modulator circuit’s block.

The input signal to the audio input module may be taken from an external microphone be

(supplied with the module) or from a cassette recorder, by choosing the appropriate switch

setting on the module. Consult the user manual for the audio input module, for further details.


Do’s:





3. Use sufficiently long connecting wires, rather than joining two or three small

ones.


Don’ts:




Experiment 4Objective: Study of Frequency Modulation Using Reactance Modulator

Equipments Required:

1. ST2203 techbook with power supply cord

2. Oscilloscope with connecting probe

3. Patch Cords

Connection Diagram:

Procedure :

This experiment investigates how ST2203's reactance modulator circuit performs frequency

modulation. This circuit modulates the frequency of a carrier sine wave, according to the audio

signal applied to its modulating output. To avoid unnecessary loading of monitored signals, X10

Oscilloscope probes should be used throughout this experiment.

1. Ensure that the following initial conditions exist on the ST2203 Module.

a. All Switch Faults in ‘Off’ condition.

b. Amplitude potentiometer (in the mixer/amplifier block) in fully clockwise.

c. VCO switch (in phase-locked loop detector block) in ‘Off’ position.

2. Make the connections as shown in figure.

3. Turn on power to the ST2203 module

4. Turn the audio oscillator block's amplitude potentiometer to its fully clockwise

(Maximum) positions, and examines the block's output (TP1) on an Oscilloscope.

This is the audio frequency sine wave, which will be used as our modulating signal. Note that the

sine wave's frequency can be adjusted from about 300 Hz to approximately 3.4 KHz by adjusting

the audio oscillator's frequency potentiometer Note also that the amplitude of this audio

modulating signal can be reduced to zero, by turning the audio oscillator's amplitude

potentiometer to its fully counter clockwise position.

5. Connect the output socket of the audio oscillator block to the audio input socket of the

modulator circuit’s block, as shown in figure.

6. Put the reactance /varactor switch in the reactance position. This switches the output of the

reactance modulator through to the input of the mixer/amplifier block~ and also switches off the

varactor modulator block to avoid interference between the two modulators.

7. The output signal from the reactance modulator block appears at TP13, before being buffered

and amplified by the mixer/amplifier block. Although the output from the reactance modulator

block can be monitored directly at TP13, any capacitive loading affect this point (e.g. due to an

Oscilloscope probe) may slightly affect the modulator's output frequency. In order to avoid this

problem we will monitor the buffered FM output signal from the mixer/amplifier block at TP34.

8. Put the reactance modulator's potentiometer in its midway position (arrow pointing towards

top of PCB) then examine TP34.

Note : that the monitored signal is a sine wave of approximately 1.2Vpp centered on 0 volts DC

This is our FM carrier, and it is presently un-modulated since the reactance modulator's audio

input signal has, zero amplitude.

9. The amplitude of the FM carrier (at TP34) is adjustable by means of the mixer/amplifier

block's amplitude potentiometer, from zero to its present level.

Try turning this potentiometer slowly anticlockwise, and note that the amplitude of the FM

signal can be reduced to zero. Return the amplitude potentiometer to its fully clockwise position.

10. The frequency of the FM carrier signal (at TP34) should be approximately 455

KHz at the moment. This carrier frequency can be varied from 453 KHz to 460

KHz (approximately) by adjusting the carrier frequency potentiometer in the reactance

modulator block. Turn this potentiometer over its range of adjustment and note that the

frequency of the monitored signal can be seen to vary slightly. Note also that the carrier

frequency is maximum when the potentiometer is in fully clockwise position.

11. Try varying the amplitude & frequency potentiometer in audio oscillators block, and also

sees the effect of varying the carrier frequency potentiometer in the mixer/amplifiers block.

12. Monitor the audio input (at TP6) and the FM output (at TP34) triggering the Oscilloscope on

the audio input signal. Turn the audio oscillator's amplitude potentiometer throughout its range

of adjustment and note that the amplitude of the FM output signal does not change. This is

because the audio information is contained entirely in the signal's frequency, and not in its

amplitude.

13. The complete circuit diagram for the reactance modulator is given at the end of operating

manual. If you wish, follow this circuit diagram and examine the test points in the reactance

modulator block, to make sure that you fully understand how the circuit is working.

14. By using the optional audio input module, the human voice can be used as the audio

modulating signal, instead of using ST2203’s audio oscillator block. If you have an audio input

module, connect the module's output to the audio input socket in the modulator circuit’s block

The input signal to the audio input module may be taken from an external microphone (supplied

with the module), or from a cassette recorder, by choosing the appropriate switch setting on the

modules.


Do’s:





3. Use sufficiently long connecting wires, rather than joining two or three small ones.


Don’ts:




Experiment 5Objective:

To study the techniques of ASK Modulation:

Preparatory Information:

Amplitude Shift Keying is the type of modulation in which a carrier is used to represent

the digital data by its presence or absence.

In the following experiment a carrier sinewave of 1 MHz is being used to modulate the

data. The modulation is being achieved by using a 2:1 Analog Mux. The logic is

illustrated below in the figure shown below.

The sinewave Sin1 is applied to the I/P1 of the Mux and the other input I/P2 is to be

connected to the ground. The data is being fed to the control input. Depending on the

control input whether it is ‘0’ or ‘1’, the switch is opened or closed and the carrier is

latched to the output. Whenever the data is ‘1’, the I/P1 i.e., sin1 is being latched to the

output, and whenever the data is ‘0’, the I/p2 is latched to the output.

Experimental procedure:1.Set up DCLT-005 in stand-alone and prepare a list of waveforms that are observed

in DCLT-005

2Connect S-CLOCK to the CODING CLOCK.

3.Connect S-DATA to the CONTROL INPUT of the modulator

4.Connect one channel of the scope to the S-Data and other to the control input.

5.Observe the control input w.r.t. the S-Data. If it is not matching with the S-Data

slightly adjust the potentiometer (P1).

6.Connect Sin1 to the Input –1 of the modulator. The amplitude of the sinewave can be

varied by means of the potentiometer (P4).

7.Connect GND to INPUT-2 of the modulator

8.Connect the scope to the CONTROL INUT test point and observe the modulated

OUTPUT w.r.t control input

Inference:

We observe that the ASK output resembles the AM signals waveforms. Only NRZ-L is used.

The performance characteristics of the AM signals and ASK signals are the same except for one

major difference i.e., in the case of AM, the modulating signal is acontinuous wave whereas in

ASK, the modulating signal is discrete in nature

Experiment 6Objective:To study the ASK Demodulation techniques

Preparatory Information:Envelope Detectors built around diode rectifiers are normally used for ASK detection.

The figure shown below illustrates a ASK detector employing a diode detector.

The diode acts as a rectifier and can be considered an “ON” switch when the input voltage is positive, allowing the capacitor C to charge up to the peak of the carrier input. During the negative half of the input, the diode is “OFF”, but the capacitor holds the positive charge previously received, so the output voltage remains at the peak positive value of carrier wave. There will, in fact be some discharge of C, producing an RF ripple on the outputwaveform, which must be filtered out. As the input voltage rises, the capacitor voltage has no difficulty in following this, but during the downward swing, the capacitor may not discharge fast enough, unless a discharge path is provided by a resistor. The resistor R does this job. The time constant of the CR has load has to be short enough to allow the output voltage to follow the modulation cycle, and yet long enough to maintain a relatively high output voltage. The Threshold detector compares the envelope (which will contain some ripple) with the reference of 5V and switches to either “HIGH” or “LOW” state thereby recovering the original data from the ASK wave.

Experimental Procedure:Maintain the connections in the DCLT-005 as in the previous experiment.

Connect the ASK output to the ASK demodulator input in the DCLT-006

Connect the Scope to the ASK input and the other channel to the data output of the

ASK Demodulator.

Observations:Observe the ASK modulated output and the modulating data in the two channels of the

oscilloscope. Also observe the “modulated carrier” at the input of “DCLT-006”. Observe the ASK

demodulated output at the DATA OUTPUT of the ASK Demodulator and compare the

Demodulated signal w.r.t to the control input.

Inference:We infer that a very small time lag between the modulating data and the recovered data which

is less than one half of the carrier time period

.

Note: If ASK Demodulated Data is not proper gently tune trim pot P1 of DCLT-006

Experiment 7

Objective:To study the aspects of Frequency Shift Keying Modulation

Preparatory Information:In this type of modulation, the modulated output shifts between two frequencies for all‘one’ to

‘zero’ transitions The two carrier sine signals are generated by employing an oscillator built

around a PLL The two signals are set to individual frequencies of 1 MHz and 0.5MHz. The

modulator is a simple 2:1 Mux that latches one of these carriers to the output

depending on the control input. The control input is driven by the modulating data which is to be

keyed and the output FSK wave represents a Carrier of 1MHz for all 1’s and a Carrier of 0.5

MHz for all 0’s.

The logic is shown below.

Experimental Procedure:Connect SIN1 to the INPUT-1 of the Modulator

Connect SIN2 to the INPUT-2 of the Modulator

Connect data to the control input of the Modulator

Connect the scope to the Control Input and the other channel to the Modulated output

Observations:Observe the FSK Modulated output and the modulating data in the two channels of the

oscilloscope. Observe the incoming modulated carrier and recovered data with respect

to the modulating data.

Inference:`Since the tracking ability and the time response of the PLL is limited, a small phase lag

exists between the recovered data and the modulating data.

Experiment 8Objective:

To study the FSK Modulation techniques using Phase Locked Loop logic:

Preparatory Information:

FSK detectors are built around PLL logics. The phase detector output of the PLL directly

gives the FSK detected output provided at least one of the modulating frequency falls

within the lock range of PLL. Refer the fig below for the block diagram

A phase Locked Oscillator can be used to demodulate a frequency shift keyed signal. The Voltage Controlled Oscillator (VCO) in the above fig. is basically a frequency modulator and oscillates at the center frequency when no signal is being received or when the modulation on the received carrier is zero. signal in frequency, and the phase detector circuit puts out a zero signal. When the incoming frequency rises because of modulation to fin+äf, the phase Comparator output creates an output signal, which drives the VCO frequency up until it again matches the fin, this time at fin+äf. The signal appearing at the input to the VCO us the sum of a fixed DC bias plus the comparator output signal. Since the oscillator shifts to higher-frequency, and for this to be true the input to it must be larger than the bias value, there must be an output from the comparator when the oscillator is tracking This means that the oscillator must be out of phase with the fin by an amount proportional to the deviation

Now if the modulation drives the received-signal frequency low, the oscillator will also beforced to move low in frequency and the Comparator output will adjust itself to the valuenecessary to produce this frequency. If the received signal frequency is varying inaccordance with a modulation signal, the value of the voltage at the input to the VCO willvary about the bias value in accordance with the modulating signal.The PLL center frequency and lock range are fixed around 1 M Hz.A low pass filter at the output will remove the carrier components from the bias voltage,leaving only the modulation signal.

Experimental procedure:Establish the same connections for FSK modulation in DCLT 005Set DCLT-005 in conjunction with DCLT 005Connect the FSK Modulated output to the FSK I/P of the FSK Demodulator (DCLT006)Connect the scope to the CONTROL INPUT and the DATA OUTPUT

Observations:Observe the FSK modulated output and the modulating data in the two channels of theoscilloscope. Observe the incoming modulated carrier and recovered data with respectto the modulating data.

Inference:Since the tracking ability and the time response of the PLL is limited, a small phase lagexists between the recovered data and the modulating data.

Note: If FSK Demodulated Data is not proper gently tune trim pot P5 (first) to your right/left and tune P2 of DCLT-006

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